This invention relates to metering valves and more particularly to an axial flow metering valve of improved design and performance.
Conventional metering valves generally have tapered or so-called "needle" valve members which are positioned closer to or farther from a correspondingly tapered valve seat by means of a metering adjustment in order to regulate flow through the valve. These metering valves, particularly those intended for use in high pressure applications, suffer from a number of difficulties in operation. One such difficulty is in maintaining consistent, precisely regulated flow which is predictable for a given metering adjustment. A source of this and other associated difficulties in many metering valves is a failure to maintain the tapered sealing portion of the valve member rigidly concentric with the valve seat. As the valve member is advanced or retracted it is permitted to undergo a certain amount of roll, pitch or yaw which affects the concentricity of the valve member with the valve seat. Such unwanted movement of the valve member occurs because of poor stabilization of the valve member and is accentuated when the valve member is subjected to high fluid pressures.
Another difficulty with many present metering valves having poppet-type valve members is that the valves become increasingly more difficult to open as a function of the system pressure due to the effective valve seat area being acted upon by the system fluid pressure. Further, many metering valves have reduced flow passage sizes compared with other types of valves and may have the valve seat and metering adjustment arranged perpendicular to the main flow axis which causes restriction and abrupt directional changes of flow and, therefore, a relatively high pressure drop. Still further, most metering valves fail to take into account unmetered reverse flow, either to check it or to provide for it.